A majority of municipal solid waste (“MSW”) is collected by trash trucks and transported to landfills where it is dumped into designated areas. When a dumping cell is full, it is sealed with a plastic sheet and covered in several feet of dirt. The buried MSW causes several environmental hazards as it decomposes, including generation of greenhouse gases (“GHG”) such as carbon dioxide (CO2) and methane (CH4).
MSW includes everyday items that are discarded by the public. For example, MSW may include biodegradable waste, inert waste, combustible construction and demolition waste, composite waste, certain types of hazardous or toxic waste, biomedical waste, and/or recyclable materials. The composition of MSW may vary greatly from municipality to municipality and may change over time. The MSW may originate from residential, commercial, institutional, and/or industrial sources.
Rather than burying the MSW in landfills, the MSW may be combusted to reduce the GHG equivalent levels below those produced through burying the MSW in landfills. Furthermore, the MSW may be combusted to recover energy from the waste. The conversion of waste-to-energy (“WTE”) may be performed at a WTE facility. The MSW may be sorted and shredded to produce refuse derived fuel (“RDF”) that is used to fire boilers that produce steam used to generate electrical power. For example, waste incinerator systems are known to generate process steam and/or electrical power while reducing MSW volume and mass. However, conventional incinerator systems often suffer from inadequate emission controls that degrade the atmosphere with hazardous air pollutants including acid gases, volatile organic compounds, and particulate matter, including heavy metals. For example, conventional incinerator systems produce high levels of nitrogen oxides (NOx), as well as oxides of sulfur (SOx) hydrochloric acid, dioxins and furans, fine particulate matter, and toxic metals, among other undesirable byproducts.
With respect to NOx formation during combustion, the three primary NOx contributors include (1) fuel NOx, (2) prompt NOx, and (3) thermal NOx. Fuel NOx is formed during combustion when a partially decomposing component specie having a carbon-nitrogen bond is oxidized, either by oxygen or a hydroxyl species. Prompt NOx follows a similar pathway to fuel NOx with a distinction that prompt NOx is typically associated with high energy density fuels such as natural gas, with free radical formation occurring within the fuel rich region of the combustion zone flame. Thermal NOx is formed at very high temperatures associated with the high energy requirement to break a nitrogen-nitrogen triple bond and enable oxidation to a NOx specie. While the reaction rates for each of these three NOx formations are different, all NOx is formed as a function of oxygen concentration and temperature. Furthermore, conventional incinerator systems produce solid residues that require special storage arrangements to prevent un-combusted organics and heavy metal contaminants from leaching into ground water. These and other drawbacks exist with conventional incinerator technology.